During radiotherapy (RT) treatments the radiation beam has to be focused on a well-defined target region and its dose has to be precisely controlled. To verify the accuracy of the radiotherapy treatment field relative to the patient, radiosensitive film, video vision systems, ion chambers and electronic portal imaging devices (EPIDs) are currently used for two-dimensional (real-time) monitoring of the applied dose. Additionally time-consuming regular quality assurance of (three-dimensional) radiation dose distribution has to be performed with specific phantoms.
Some of the relevant characteristics of currently used radiation treatment field verification/dosimetry techniques are:                Ion chamber (low resolution, slow, non-integrating dose measurement),        Video chain (cumbersome, not geometrically accurate, bad efficiency),        Film (critical work-flow, lower sensitivity than EPID),        EPID (expensive, dead-pixels).        
U.S. Pat. No. 5,633,584 describes gel in a container in which a MRI visualizable permanent image is formed in response to ionizing radiation. The image is representative of the dose distribution of the energy to which the gel is exposed. The image can be used for dosimetric purpose; to provide reference standards for quality control of magnetic resonance imaging techniques and equipment; and as a three- or two-dimensional array detector in industrial radiography.